Scattered primary and conditionally immortalized neuroepithelial cells transplanted into the embryonic rat brain differentiate into neurons and glial cells

arlier studies suggested that stem cells from one somatic tissue may generate differentiated elements of another, embryologically unrelated, tissue after an exchange in their positions through transplantation. Two reports indicated that murine and human neural stem cells of clonogenic origin after in vitro expansion in growth factor-supplemented media, may sustain hematopoiesis when injected into sublethally irradiated mice. Here we investigated if freshly dissociated fetal neural cells (fNC) share the reported hemopoietic potential of in vitro expanded neural cells. In order to minimize the risk of hemopoietic contamination, donor cells were taken from mouse E10.5 developing brains, before completion of blood vessel ingrowth into the brain; 106 fNC derived directly from fetal brains of transgenic mouse expressing an enhanced version of the green fluorescent protein were injected into the tail vein or directly into the bone marrow of sublethally irradiated (6 Gy) C57B16 mice. After transplantation, the presence of donor-derived cells was assessed at different survival times by FACS analysis, PCR, and clonogenic stem cell assays on peripheral blood and bone marrow. While bone marrow-derived cells were detected from 2 weeks onward after grafting, none of the mice grafted with neural embryonic cells demonstrated any sign of transdifferentiation into hemopoietic cells up to 16 months after transplantation. Our data indicate that ability to transdifferentiate from neural into the hematopoietic phenotype, if present, is acquired only after in vitro expansion of neural stem/progenitor cells and it is not present in vivo.